Networking problems


On our company there are three LANs with different IP ranges. On one LAN there are new servers, on other LAN there are old servers and on the third lan there are the clients. Clients are Windows based and servers are Windows and linux based (windows mostly).

We currently have a problem. When making ping from a Linux server on the old lan I can see 50% packets lost and 50% packets DUP. If I make a traceroute I can see just 2 jumps: one from old server to router and one from router to new server.

We are also experimenting some intermitent connecting problems from clients to new server.

What can I do? Any idea to help me to diagnose and solve this problem?

Thanks in advance.
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Mohammed KhawajaManager - Infrastructure:  Information TechnologyCommented:
Not enough information is provided, could you provide the following information:

1.  Make and model of switches
2.  Make and model of router
3.  Number of clients/devices involved
4.  Connection speed for each client

What I believe is happening is that your router interface is most likely 100 mbps (if not 10 mbps) and it cannot keep up with the requests.  Also check your switches to ensure there are no errors on any ports (issues such as speed, duplex settings, etc. can also cause issues).
gplanaAuthor Commented:
I think all are 1000mbps (1gbps). I think they are cisco but not sure which model. I will ask to my system administrator for the configuration of ports on switches/routers.
gplanaAuthor Commented:
Our expert on system area has restarted all routers, switches, servers, etc... and now all seems to work fine. Does this makes sense?
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gplanaAuthor Commented:
Also he said that a Linux server we had is not well prepared for VLANs so this is why he had some network problems sometimes (but not always). Does this makes sense?

I think VLANs are created on new server's LAN but not on old server's LAN, where our Linux server is connected, so shouldn't be VLANs transparent to our Linux server?
It could be that there was a bad configuration that was not saved on one of the routers/switches.  Restarting a router/switch will reload the last saved configuration.  It could also be that one of the routers/switches was caching something that was causing a problem.

".... so shouldn't be VLANs transparent to our Linux server? " 

Well, sort of, but not really.  VLAN's are nothing more than a few extra bytes in the Ethernet header that contains the VLAN number this frame is part of; these are called tagged frames.  Any frame without this is untagged.

If you changed your switch so that you were sending tagged frames to a host that was not configured to accepted/recognize tagged frames, that host will drop the tagged frames.  

It sounds like the network was changed to tag frames and send to some of the Linux hosts and those hosts were not re-configured to accept the tagged frames, so they were just dropping them.
gplanaAuthor Commented:
Thanks for your answer.

I  now understand the point about tagged/untagged frames. However, if my Linux server doesn't accept tagged frames, then any of the ip packets would be received right? The problem is that some packets are lost and some are duplicated, but some of them are received, and our application works well sometimes, and doesn't work some times (because of this connect issue).
Mohammed KhawajaManager - Infrastructure:  Information TechnologyCommented:
The packets will make it to the NIC but the NIC will discard it as it cannot decipher the content.  The only way your LINUX will accept all VLAN traffic is if the port for your NIC is configured as a trunk port and you configure sub-interface for each VLAN you want your LINUX to accept traffic from.  This is also how multi-homed servers with one NIC also works.
gplanaAuthor Commented:
Sorry Mohammed, but I'm not understanding you. This linux server has just one NIC, connectad to a "normal" LAN (not VLAN). Then this LAN is connected to some VLAN.

Also application is working fine after restarting the switches/routers. So I guess the problem is not on the Linux server, am I right?
It all depends on how the port that the Linux server is connected to is configured.

If the switch port is configured so that the frames are untagged, then the Linux server can be configured "normally."

If the switch port is configured so that the frames are tagged, then the Linux server must be configured so that it is VLAN aware.

On Cisco switches if the port is configured as a access port, this is untagged.  If it is configured as a trunk port, then the frames are tagged, except for the VLAN that is the "native" VLAN which by default is VLAN 1.

Some other switches also use the terms access port and trunk port for untagged and tagged VLAN's.  

HOWEVER, some switches use the term trunk to describe combining multiple physical ports into a single logical port, which Cisco calls Etherchannel/port channel.

It would help to know what brand switches you have.

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